Aspects of the present inventive concept relate to a shroud impeller used for a centrifugal compressor, and more particularly, to a shroud impeller of a centrifugal compressor, which can be simply manufactured with a high processing yield rate, high structural stability, and high size precision, and a method of manufacturing the same. In general, a centrifugal compressor signifies a device for compressing a fluid by converting kinetic energy into pressure energy through a centrifugal force by sucking the fluid in a rotational axis direction of a high-speed rotor or an impeller and circumferentially exhausting the fluid.
The centrifugal compressor has been extensively applied to various industrial fields such as various types of air conditioning facilities and gas turbine systems.
As shown in FIG. 1A, a general centrifugal compressor includes an impeller 10 having a rotary hub 11 connected to a driving shaft 40 and a plurality of blades 12 radially provided about a rotational axis X-X′ of the rotary hub 11.
In addition, the centrifugal compressor includes a housing 20 formed with an inlet into which a fluid to be compressed is introduced and an outlet through which the compressed fluid is discharged and provided with an inner surface 21 fixedly adjacent to the blades 12 and a diffuser 30 that reduces a dynamic pressure component of a voltage component increased due to force received from the impeller 10 and increases a static pressure component thereof.
An impeller used for the general centrifugal compressor constructed as described above is classified into an open impeller and a shroud impeller according to the capacity and performance thereof.
That is, as shown in FIG. 1B, an impeller where outer ends of the blades 12 are open may be called an open impeller 10 or an unshrouded impeller having no shrouds. Since the outer ends of the blades 12 are open in the open impeller 10, mechanical processing is possible so that the open impeller 10 can be easily manufactured. In addition, precise profile tolerance may be ensured so that a structure of the open impeller 10 is stable and a manufacturing cost of the open impeller 10 is relatively low.
However, since the outer ends of the blades are open in the open impeller 10, the open impeller 10 has weak strength insufficient for a gas turbine which rotates at a high speed.
Further, the open impeller 10 represents problems in that some of a compressed fluid is leaked through a gap formed between an outer end of the blade and an inner surface of the housing so that flow loss occurs. In addition, the flow loss is significantly increased due to leakage in an inlet A and an outlet B of the housing 20.
In order to solve the above problems of the open impeller, a shroud impeller 10 has been suggested as shown in FIG. 2. The shroud impeller 10 includes a shroud 13 that connects outer ends of a plurality of blades 12 provided in the rotary hub 11 to each other while surrounding the outer ends of the blades 12.
In the shroud impeller 10, a closed fluid path for a fluid to be compressed is formed by adjacent blades 12 and the shroud 13 so that flow loss may be reduced as compared with that of the open impeller, thereby representing higher compression efficiency.
Further, the shroud 13 serves as a reinforcing structure connecting the blades 12 to each other so that the shroud impeller 10 has strength higher than that of the open impeller.
However, in order to form a path of a fluid to be compressed inside the shroud, the shroud impeller has a very complicated three-dimensional structure so that processing is not easy and a manufacturing cost is considerably increased.
Meanwhile, according to the scheme of manufacturing a shroud impeller according to the related art, an impeller including a shroud is manufactured by a casting scheme or after an open impeller is manufactured by a Hot Isostatic Press (HIP) scheme, the open impeller is mechanically processed and a separate shroud is welded thereto.
However, the impeller manufactured through the casting scheme or the HIP scheme may have a weak strength due to a characteristic of a manufacturing method and the impeller is easily deformed or damaged upon pressure variation.
Further, when the separate shroud is welded, the whole shroud is restrictively welded to a plurality of blades so that a welded region may be easily damaged or broken as pressure is applied thereto.
As a related art of the shroud impeller, FIG. 2A shows a method of mechanically processing a monolithic rotor having a disc shape by a cutting tool 50 controlled using a numerical control tool, which is disclosed in U.S. Pat. No. 7,305,762. However, the above patent may not be compatible with a complicated inner fluid path, and there is a limitation in processing due to a shape of the cutting tool.
Further, FIG. 2B shows a method of manufacturing an impeller by bonding an upstream impeller member and a downstream impeller member to each other after the upstream impeller member and the downstream impeller member are separately processed, which is disclosed in Japanese unexamined patent publication No. 2010-121612 (hereinafter, referred to as patent document 1).
In order to solve the above problem, as disclosed in U.S. patent publication No. 2011-0318183 (hereinafter, referred to as patent document 2), a technology of forming an integral shroud in a blade, and forming a partially divided shroud, and bonding the blade to the integral shroud by brazing welding, stick welding, ultrasonic welding, or electron beam welding has been suggested.
However, in the case of patent document 1, an error may occur when bonding a plurality of members which are separately processed so that it is difficult to maintain accurate shapes of a blade and a shroud. In addition, strength of a bonding part is so low that patent document 1 is not suitable for a compressor of a gas turbine which is rotated at a high speed.
In the case of patent document 2, although strength may be improved by divided shrouds bonded to an integral shroud, processing of the divided shroud is complicated and a bonding work is significantly complicated and inconvenient.
Furthermore, if the divided shrouds are not precisely and accurately bonded and thus an error occurs, dangerous situation may be caused when the impeller is used for a gas turbine rotated at a high speed.